今天在進行專案去O改造的時候遇到了一個oracle資料庫和pg資料庫相互轉換的問題：oracle資料庫的start with connect connect by prior這個是用來進行樹形查詢的語句
測試如下：

drop table sr_menu;
create table sr_menu(  
  id number(10) not null, 
  parent number(10),
  title varchar2(50)
);
insert into sr_menu values (1, null, 'level 0');
insert into sr_menu values (2, 1, 'level 1');
insert into sr_menu values (3, 1, 'level 1');
insert into sr_menu values (4, 1, 'level 1');
insert into sr_menu values (5, 3, 'level 2');
commit;

select * from sr_menu;

        ID     PARENT TITLE                                             
---------- ---------- --------------------------------------------------
         1            level 0                                           
         2          1 level 1                                           
         3          1 level 1                                           
         5          3 level 2                                           
         4          1 level 1
select * from sr_menu 
start with id = 1 
connect by prior id = parent;
        ID     PARENT TITLE                                             
---------- ---------- --------------------------------------------------
         1            level 0                                           
         2          1 level 1                                           
         3          1 level 1                                           
         5          3 level 2                                           
         4          1 level 1  
 

上面程式碼，start with 會先根據id為1開始查詢他的子節點，在根據查出來的節點查下一層子節點知道查詢完成。
改造成pg資料庫的時候是使用 with recursive

WITH RECURSIVE a AS (
SELECT id, parent, title
  FROM sr_menu
  WHERE id = 1
UNION ALL
  SELECT d.id, d.parent, d.title
  FROM sr_menu d
  JOIN a ON a.id = d.parent )
SELECT id, parent, title FROM a;

 id | parent |  title
----+--------+---------
  1 |        | level 0
  2 |      1 | level 1
  3 |      1 | level 1
  4 |      1 | level 1
  5 |      3 | level 2